Is aircon gas flammable? (A comprehensive overview)

Is Air Conditioning Refrigerant Flammable?

It depends, some of them are flammable, some are slightly flammable and some are non-flammable. The most commonly used refrigerants are considered slightly flammable (R-32, R-22 and, R-410a). 

That being said, refrigerants in air conditioning systems are contained in highly pressurised cylinders, and pose a risk of explosions if the cylinder is damaged or excessively heated.

Many refrigerants are dangerous if inhaled or if in contact with skin, some may also produce highly toxic phosgene gas if subjected to flames. For the proper safety measures, the safety data sheet of the specific refrigerant must be consulted.

The cause of accidental fires in air conditioning systems is often electric malfunction, inappropriate installation or overheating due to lack of maintenance.

Is the R-32 Refrigerant Flammable?

R-32 refrigerant is considered slightly flammable. It is categorised as A2L by ASHRAE. It is classified as A2L – slightly flammable by ASHRAE.

However, in air conditioning systems R-32 is kept pressurised, therefore it is at a risk of causing explosions if the cylinder is at too high of a temperature.

As mentioned above R-32 is considered only slightly flammable. However, difluoromethane, the major component of R-32, is considered highly flammable.

R-32 refrigerant is also called, R-32, Freon 32, difluoromethylene, HFC-32.

R-32 Refrigerant General Properties

At ambient conditions R-32 is a colourless gas, with low solubility in water. Below some physical properties of R-32 are listed.

PropertieValue
Chemical formulaCF2H2
Molar mass52.024 g/mol
Density at 25 °C and 1 atm1.1 g/cm3 (liquid state) 
Melting point at 1 atm−136 °C 
Boiling point at 1 tm−52 °C
Vapour pressure1518.92 kPa (at 21 °C) 
Ozone depletion value0
Autoignition temperature at 1 atm648 °C

Is the R-22 Refrigerant Flammable?

R-22, by itself, if in contact with air or another oxidising material it can become combustible.

R-22 is also known as HCFC-22, by its chemical names chlorodifluoromethane or difluoromonochloromethane or just by its chemical formula CHClF2. It is a colourless gas at ambient pressure. It has been widely used as a propellant and a refrigerant. 

Since it is an HFCs gas, known for damaging the ozone layer, its use is being reduced in the European Union and in the United States.

Some R-22 Refrigerant General Properties

Below some general properties of the R-22 refrigerant are listed.

PropertieValue
Chemical formulaClF2CH
Boiling point at 1 atm−40.7 °C
Molar mass86.47 g per mol
Density at 1 atm and 15 °C3.6 kg/m3
Odoursweetish
Hazard statementsH380, H420
Ozone depletion potential0.55
Autoignition temperature632 °C

This gas has a high global warming potential (GWP) of 1810, meaning it is 1810 times as powerful as carbon dioxide.

Is the R-410A Refrigerant Flammable?

R-410A is considered slightly flammable. It consists of a (50:50) of R-32 (difluoromethane) and R-125 (pentafluoroethane).

As with most compressed gases in cylinders, it has the danger of explosions if under high heat or if damaged.

Some R-410A General Properties

R-410A can also be named AZ-20, Puron, among others.

PropertieValue
Boiling point−48.5  °C
Vapour density at 30 °C3.0 Kg/m3
Flash pointN/A
Autoignition temperatureApproximately 790 °C

Other Air Conditioning Refrigerant Gases

Since the above mentioned refrigerant gases are either ozone depleting or have a high global warming potential. Other refrigerants are considered, these include some hydrocarbons, ammonia and carbon dioxide.

Hydrocarbon Based Refrigerant Gases

As a pretty general rule any hydrocarbon that is liquid or gas at ambient temperature and pressure is flammable or highly flammable. Commonly found hydrocarbon refrigerants are listed below:

  • Isobutene (R-600a)
  • Propane (R-290)
  • Propylene (R-1270)

Some consider hydrocarbon refrigerants as an alternative to fluoro containing refrigerants, since hydrocarbon refrigerants are far less persistent in nature.

Ammonia as a Refrigerant Gas

Ammonia (NH3) is a good refrigerant, however it poses a considerable danger for explosions and is rarely used in air conditioning systems.

Carbon Dioxide as a Refrigerant

Carbon dioxide (CO2) is a relatively quite safe refrigerant, it is only toxic in high concentrations and it is non flammable. 

But in order for carbon dioxide to be effectively used as a refrigerant, a lot of energy is required since it has a  critical temperature of 31 ℃ and high critical pressure of 7.370.000 Pa.

Refrigerant Cylinder Colour Code

The American Society of Heating, Refrigerating, and Air Conditioning Engineers association (ASHRAE) has established a series of guidelines with standards for refrigerants.

Refrigerants should have their name starting with an ‘R’ followed by two or three numbers (these numbers indicate the molecular formula of the refrigerant). 

Some refrigerants may have a letter at the end of their name. If the letter is in lower case, it means the refrigerant is a specific molecular isomer. If the letter at the end is in upper case, it indicates that the refrigerant is a mixture.

Until 2020 the recommendation given by ASHRAE was to use a specific colour for the cylinders of each different refrigerant. This way they could be easily recognized. However, following these recommendations was not a law.

From 2020 onwards, the new recommendation is to use  grey colour for the cylinder of any refrigerant, and use different colours for each different refrigerant on the label of the cylinder.

More information regarding recommendations by the ASHRAE can be found on their website.

Brief Explanation on how Air Conditioners Works

The process of transferring heat from a place to another results in the cooling of one and heating of the other. When an air conditioning system is used to cool a place, a refrigerant within the air conditioning system is cooled to low temperatures. The refrigerant is then heated by the heat of the external area. Resulting in heating of the refrigerant and cooling of the external area.

Heat Transfer in a Room Connected to an Air Conditioner

As a general rule in thermodynamics, heat is transferred from hotter bodies to colder bodies. For a hot room to be cooled, its heat must be transferred to the refrigerant in the air conditioner.

Air conditioning systems vary, as an example a vapour compression cycle is discussed. A simple vapour compression cycle can be thought of as starting with the refrigerant in the liquid state, when the  heat from the room is in contact (transfer of heat occurs by conductivity) with the refrigerant, heat is transferred from the room to the refrigerant. 

That causes the refrigerant to vaporise. That vapour is then compressed giving off heat to the exterior and causing the refrigerant to liquify. And the cycle can start over. The energy required to compress the refrigerant vapour into liquid usually is from an electric source.

Conclusions

Some properties of the refrigerating gases R-22, R-32, and r410a have been discussed.

There is a wide variety of refrigerants available for use in air conditioners. It is always important to consult the proper safety measures.  

The environmental importance of these gases was discussed. Possibilities for the future of refrigerating gases were presented.

Some of the dangers associated with air conditioners were discussed as well.

Frequently asked questions (FAQ): Is aircon gas flammable?

Can AC gas catch fire?

Fires involving air conditioners are most often caused by complications in the electric parts. Fires can also be caused by fluctuations in the voltage. Lack or poor maintenance can also lead to issues that could cause overheating. Dust accumulation in the venting parts can also lead to problems. That being said if the air conditioner in question uses a flammable refrigerant such as hydrocarbons, an incident leak of said refrigerant may cause fires.

Is gas from AC dangerous?

That depends on what the gas is composed of and at what concentration it is present. The gas may beThe coolant leaking from an aircon rapidly evaporates into a gas. This gas can be inhaled if a leak happens or during gas exchange. If it’s the case, leaking of the gas may expose users to prolonged exposure. In those causes there is also a high risk for health hazards.

Which AC gas is flammable?

They are all mostly at least slightly flammable. In general, hydrofluorocarbon, chlorofluorocarbons and hydrochloroflurocarbons are less flammable than hydrocarbon refrigerants. Ammonia is also flammable.

Can an AC compressor explode?

Yes, if too much dust and dirt accumulates on the condenser coil, the air conditioning venting system may not be able to release the absorbed heat. That increases both the temperature and the pressure in the whole system, including the cylinder that contains the compressed refrigerant. That could lead to an explosion.

Is there any completely safe air conditioning refrigerant gas?

The safer refrigerant gas could be carbon dioxide, since it is not flammable under pretty much any circumstance. It also has very low toxicity. The main problem with carbon dioxide as a refrigerant is that it requires too much energy and a sophisticated system to operate in air conditioners.

Which refrigerant is not allowed to be vented?

According to section 608 it is illegal for individuals to intentionally vent ODS refrigerants (including CFCs and HCFCs) and their substitutes (such as HFCs), while maintaining, servicing, repairing, or disposing of air- conditioning or refrigeration equipment.

Are air conditioning refrigerant gases ozone depleting gases?

Refrigerants that contain at least one hydrochlorfluorocarbon or chlorofluorocarbon substance are damaging to the ozone layer. Fluorocarbon based refrigerants are mostly not damaging to the ozone layer, but many of them have a very high global warming potential.

References

Refrigeration, Air Conditioning and Heat Pumps Book • Fifth Edition • 2016

The Montreal Protocol on Substances that Deplete the Ozone Layer. UNEP, 2000. ISBN 92-807-1888-6

https://www.ahrinet.org/App_Content/ahri/files/Guidelines/AHRI_Guideline_N_2017.pdf

Yun-Ting Tsai, Jian-Yao Liao, Chi-Min Shu, Explosion characteristics of chlorodifluoromethane and isobutane at high temperature and pressure using a 20-L apparatus, International Journal of Refrigeration, Volume 96, 2018. Pages 155-160. https://doi.org/10.1016/j.ijrefrig.2018.08.022

Wang Zhang, Zhao Yang, Jin Li, Chang-xing Ren, Dong Lv, Jie Wang, Xin Zhang, Wei Wu,

Research on the flammability hazards of an air conditioner using refrigerant R-290,

International Journal of Refrigeration, Volume 36, Issue 5, 2013, Pages 1483-1494.

https://doi.org/10.1016/j.ijrefrig.2013.03.015

Safety data sheet for R-410A can be found here.

More information on refrigerants can be found here.

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